Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al. and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
In known printing systems having an intermediate imaging member, such as ink printing systems, the print process includes an imaging phase, a transfer phase, and an overhead phase. In offset ink printing systems, the imaging phase is the portion of the print process in which the ink is expelled through the piezoelectric elements comprising the print head in an image pattern onto the image drum or other intermediate imaging member. The transfer or transfix phase is the portion of the print process in which the ink image on the image drum is transferred to the recording media. The overhead phase is the portion of the print process after the imaging phase in which the operation of the intermediate imaging member and the transfer roller are synchronized in preparation for the transfer of the image from the image drum or intermediate imaging member. The overhead phase may sometimes include the portion of the print process after the imaging phase in which the imaging member is synchronized in preparation for the next imaging phase. In some printers any of these three phases may overlap one another in real time.
Many of the imaging systems that implement the current process described above provide a print head controller with a reflex clock to control registration of the ink image on a media sheet or offset print member. The reflex clock times the firing of the print head jets in accordance with timing signals generated from a position based measurement of the imaging surface. This is typically done with a rotary encoder or the like. Imperfections in offset member runout, encoder alignment, and other known eccentricities, cause cyclic errors in the encoder position signal that result in registration position errors. To address these position errors, techniques have been developed for print head controllers to learn the cyclic errors and incorporate an offset signal to compensate for these cyclic errors. Systems that implement these compensation techniques are disclosed, for example, in U.S. Pat. No. 6,076,922 to Knierim and U.S. Pat. No. 6,215,199 to Markham.
While these known compensation systems are useful for cyclic errors, other types of errors may be introduced into the imaging system that affect the registration accuracy. Some of these errors include physical disturbances that arise from the interaction of components in the imaging device. For example, a number of mechanical subsystems interact with a print drum in some printing processes. These mechanical subsystems include a transfer subsystem, a release agent subsystem, and a wiper blade. The transfer subsystem includes a transfer roller that is moved into engagement with the print drum to form a nip through which a sheet of media is pressed to transfer the image from the print drum to the media sheet. The impact of the transfer roller on the print drum, the application of pressure against the print drum, and the release of that pressure, may cause a disturbance, which results in a registration error. Likewise, the movement of a release agent applicator into and out of engagement with the print drum may also result in registration errors. As these errors arise from the physical disturbance of the print drum from subsystem interactions rather than eccentricities in the manufacture of the print head and related components, the above-identified compensation systems cannot make the required adjustments for correcting these errors.